1. Field of the Invention
The invention relates to catheters for semi-selectively injecting a radiopaque material or contrast medium into coronary arteries, including natural coronary arteries and surgically grafted bypass arteries, for radiological diagnostic purposes.
2. Description of the Prior Art
In coronary angiography, a tip of a catheter is inserted into a brachial, axillary or femoral artery and from there advanced into the portion of the aorta proximal the coronary ostia. Techniques for opacification of the coronary arteries can generally be divided into three groups, namely, (1) non-selective, (2) selective, and (3) semi-selective. In the non-selective technique, the catheter is positioned in the aorta valve cusps area which is then flooded with contrast medium, a portion of which passes into the coronary arteries. In the selective technique, the tip of a catheter is inserted directly into the ostium of each coronary artery and contrast medium is injected directly into each artery. In the semi-selective technique, a catheter tip is positioned within the aorta adjacent to the coronary ostia with one or more openings of the catheter directed toward the aorta wall so that injected contrast media is more concentrated in the outer portion of the aortic stream adjacent to the coronary ostia.
Past coronary angiography of the natural coronary arteries has been, for the most part, generally performed by successively employing two or three different catheters, the first being employed in a non-selective technique and the last one or two being employed in selective techniques. The first catheter is a generally straight catheter with an open end and a plurality of spaced sidewall openings adjacent the open end. This open end of the catheter is positioned within the aorta just above the aortic valve. Injection of contrast medium is utilized to flood the aortic cusp area and pinpoint the openings to the coronary arteries. From fluoroscopic or angiogram information gained from the first procedure, a general purpose selective catheter or successive left and right selective coronary catheters are inserted with the tip or tips being successively inserted into the corresponding left and right coronary arteries to inject contrast media therein and to enable diagnostic coronary angiograms. The selective opacification of the coronary arteries produces sharp images and pictures which are then utilized in diagnosing and treating or surgically correcting a coronary problem.
The generally employed past coronary angiography procedures have substantial deficiencies in being costly and involving considerable risk. The procedures for inserting two or three successive catheters in a leg or arm artery generally require the use of a sheath which generally must be installed in the artery under hospital operating room conditions with pre- and post-operative care. The selective catheterization of the coronary arteries has disadvantages including requiring a large amount of time to position the catheter tips in the coronary ostia, failure of the catheter to enter a coronary ostium due to a stenoic condition or an anatomical abnormality, blocking blood flow into a coronary artery to cause heart damage or malfunction such as asystole or arhythmia, creating a coronary occlusion by passing an embolus from the catheter into the coronary artery or by dislodging an arteriosclerotic plaque from the coronary wall, or otherwise damaging a coronary artery. In diagnostic coronary angiography, approximately 30% of all patients are found to have no significant coronary artery disease. There is a general need to reduce costs and risks to patients undergoing coronary angiography by employing less costly and less risky procedures. Substantial improvement could result from employment of such procedures in screening techniques to reduce the number of patients requiring the more extensive and risky procedures.
Percutaneous catheterization is less traumatic on the patient and easier to perform than procedures requiring the insertion of a sheath. In percutaneous catheterization, a needle is first inserted into the artery (brachial, axillary or femoral) and a guide wire is inserted into the vessel through the lumen of the needle. After the needle is withdrawn over the guide wire, the catheter is threaded over the guide wire into the vessel where, under fluoroscopic guidance, the tip of the catheter and guide wire are advanced into the aorta. After the guide wire is removed, withdrawal of a portion of blood to flush the catheter and controlled continuous drip of heparinization solution prevent clot insertion and formation. Where one or more additional catheters must be used, percutaneous insertion of the additional catheters into the same entry point has a high risk of creating a large tear in the artery; thus employment of a sheath is generally preferred in multiple catheter procedures.
Semi-selective catheterization including use of loop catheters has been previously studied for use in coronary arteriography, such as described in Bellman et al., "Coronary Arteriography". The New England Journal of Medicine, Vol. 252, No. 7, Feb. 18, 1960, pages 325-328; Williams et al., "Coronary Arteriography", The New England Journal of Medicine, Vol 252, No. 7, Feb. 18, 1960, pages 328-332; and Amplatz, "Percutaneous Arterial Catheterization and Its Application", Radiology Vol. 87, No. 2, February 1962, pages 265-275. These catheters have a simple loop tip in a plane at right angles to the long axis of the catheter with three side holes drilled equidistantly apart in the loop so that one hole would lie opposite each coronary sinus of Valsalva in nearly any position of catheter rotation. Contrast media is injected under pressure through the outward facing holes in the loop into portions of the aortic stream juxtamural to the coronary ostia. The obtainment of good or excellent quality angiograms were initially reported. This loop catheter technique for coronary opacification has the advantage that the catheter can be inserted into an arm or leg artery by percutaneous catheterization which can be performed by a radiologist without hospital operating conditions and with substantially less pre- and post-operative care. Also this semi-selective technique involves less risk than selective techniques due to a reduction in the possibility of the catheter blocking a coronary ostium, a reduction in the number of catheter insertions and thus a reduction in chances of clot formation and insertion, and reduction in the possibility of damaging the coronary artery or dislodging arteriosclerotic plaque.
In spite of the cost saving and the inherent greater safety of semi-selective catheterization using a coronary loop catheter, it has not achieved commercial success and has not replaced any notable portion of the employment of non-selective and selective coronary catheterization procedures. As reported by Paulin, "Coronary Angiography", Acta Radiologica, Supplementum 233, Stockholm 1964, employment of the single loop coronary catheter often failed to attain uniform opacification of both coronary arteries, and almost always showed signs of loop displacement during injection of contrast medium. The severe deficiencies of the single loop design led to the development of a double loop tip design constructed counterclockwise from the straight body portion with five side holes placed equidistantly along the periphery of the loop and which was reported to have superior stability and result in greater improved opacification of both coronary arteries. This prior double loop design, like the prior single loop design, has failed to achieve any notable commercial success.
In coronary angiography of surgically grafted bypass arteries, selective catheterization techniques are generally employed. Generally radiopaque rings are secured on the bypass vessels adjacent their connection to the aorta, and these rings are used to guide the radiologist, or cardiologist, in positioning of a selective catheter tip into the ostium of a grafted vessel, without the help of prior non-selective opacification. The selective catheterization of bypass arteries also has a higher risk of blocking the artery and requires more time for catheter placement than a semi-selective technique.
A recent radiology development concerns the increasing employment of computerized radiology techniques including digital subtraction angiography (DSA) wherein arterial images taken during injection are enhanced by subtraction techniques. Subtraction of base image portions enables the production of sharp high contrast angiograms electronically on a cathode ray tube with the employment of less contrast medium and less exposure to X-rays than has been possible in the production of film images by direct X-ray exposure. However, DSA has thus far been unable to effectively image the natural coronary arteries with intravenous and non-selective low volume aortic root injection. In the latter situation the contrast delivery is particularly inefficient as most of the injected contrast medium is immediately washed out by the ascending aorta flow.